The present invention relates to microalgae culture systems.
Microalgae and seaweed are valuable aquaculture crops, as they remain prominent in the culture of many aquatic animals, especially marine species. In particular, microalgae production is extremely important to the successful production of seed stock in the marine shrimp farming industry and in the bivalve farming industry. Many species of fish consume algae as adults and receive indirect benefits of algae in their tanks. In addition, the intensive larviculture of many species of marine fish depend on large supplies of rotifers, which are generally raised on microalgae. Needs exist for cost and time efficient systems for culturing microalgae on a consistent and reliable basis.
Current methods for culturing phytoplankton are of three basic types: continuous, semi-continuous and batch. Continuous cultures are steady-state continuous flow cultures in which the rate of growth is governed by the rate of supply of the limiting nutrient. Continuous culture systems are generally delicately balanced, often axenic, are harvested continually and receive constant nutrient replenishment. The rate of washout in continuous culture systems must be adjusted such that the rate of harvest is slightly slower than the maximum specific growth rate. While continuous cultures are efficient and provide for a consistent supply of high-quality cells, existing continuous culture systems are only feasible for the production of relatively small amounts of microalgae.
Semi-continuous cultures and batch cultures are used when large quantities of algal biomass are required. In semi-continuous cultures, a given population is allowed to grow until a desired cell density is achieved, at which time the culture is partially harvested and a fresh medium is added. The culture is repeatedly grown up and harvested. Semi-continuous cultures are mainly indoors, as outdoor conditions render the duration of the culture unpredictable. Competitors, other contaminants and predators eventually build up, rendering the culture inviable. Cells produced using semi-continuous culture systems tend to vary in nutritional quality.
Batch cultures differ from continuous and semi-continuous systems in the area of harvesting. In batch cultures, when the population reaches its maximum or near-maximum density, the culture is completely harvested. Batch cultures are extremely inefficient and often result in inconsistent quality.
Needs exist for microalgae culture systems that have the production capabilities of batch or semi-continuous systems and the consistency and efficiency of continuous systems.
Compounds which are active against several drug resistant pathogenic bacteria have been isolated from the Chaetoceros sp. microalgae. Needs exist for methods and systems for producing mass quantities of Chaetoceros sp. microalgae for use in developing antibiotics.
Vibrio vulnificus contamination is currently a major problem facing the oyster farming industry. The U.S. Food and Drug Administration has recently banned oyster harvests from the Gulf of Mexico during the summer months due to Vibrio vulnificus contamination of the oysters. Studies demonstrate that Chaetoceros sp. microalgae is active in vitro against pathogenic Vibrio vulnificus. Needs exist for mass cultivating methods that allow for oyster depuration systems that take advantage of Chaetoceros sp. activity against Vibrio vulnificus to cleanse the oysters of that pathogen.
Existing methods for mass cultivating Chaetoceros sp. and other microalgae have proven inadequate. The primary difficulty in culturing Chaetoceros sp. microalgae is that undesirable species contaminate and outcompete Chaetoceros sp. microalgae in culture vessels and outdoor algal systems. Costly water treatment systems are necessary in existing system to filter out predators, competitors and disease from the culture media before the media is used to culture the microalgae.
Existing indoor and outdoor microalgae culture systems are unacceptable. Existing indoor cultures produce small volumes of algae under controlled conditions. Illumination, temperature and nutrient levels are controlled within strict levels, allowing for predictable growth. Early stages of existing large outdoor unialgal cultures are generally grown indoors. Many indoor closed cultures are axenic, or free of foreign organisms such as bacteria. However, axenic cultures require scrupulously sterilized glassware, tubing, water, pipettes, nutrient, media, etc. to avoid contamination. While axenic cultures are less prone to failure than outdoor systems, they are prohibitively expensive for commercial operations for producing large volumes of microalgae.
In efforts to limit contamination and predation, many existing methods include a scaling up process, whereby small, test tube cultures are gradually transferred to larger culture vessels having the desired harvest volume. That process often takes upwards of two weeks to complete, is labor intensive, and must be conducted in sterile rooms with artificial lighting and cooling to avoid contamination by competing microalgae species.
Needs exist for relatively inexpensive, non-labor intensive methods and system for mass cultivating Chaetoceros sp. microalgae.
The present invention is an open, continuous microalgae culture system that optimizes culture conditions for microalgae, such as Chaetoceros sp. marine microalgae, in a cost effective manner. The system provides for faster and more efficient microalgae culturing than existing methods and systems. In the present invention, Chaetoceros sp. exemplifies the microalgae culture system and is not limited to that species alone.
In contrast to the widely used indoor cultivation systems described in the background, the present system establishes optimal culture conditions for Chaetoceros sp. microalgae and provides for the outdoor culturing of the microalgae. No water treatment systems are needed as the Chaetoceros sp. microalgae outcompetes other species of microalgae in the culture. The present invention provides for the continuous mass cultivation of Chaetoceros sp. microalgae in large outdoor containers using natural sunlight. By harvesting a portion of the culture periodically (i.e., each day) and replacing the harvested volume with new, non-sterile culture media such as seawater, the present system incurs no xe2x80x9cdown timexe2x80x9d and allows for the continuous production of Chaetoceros sp. microalgae in mass quantities. Labor, utility and equipment expenses are minimized in the present system, as sterile conditions and artificial culturing apparatus are not required.
Advantages realized by the present open Chaetoceros sp. microalgae system include:
low initial capital expenses
small land area requirements
minimal labor requirements
low electricity requirements
a sterile room is not needed to store test tube cultures of pure strain single species Chaetoceros sp. microalgae
a single outdoor tank is included.
The initial capital expenses and the land use are much less than in existing systems since just a single, unprotected outdoor tank produces what in traditional algal culture requires a series of indoor protected tanks, an artificial light source, a sterilized water source and a sterile culture room for test tube cultures. Labor savings result from not having to transfer the cultures into a series of larger tanks as well as not having to maintain test tube cultures of Chaetoceros sp. microalgae.
The present culture system and method have immediate applications in marine shrimp hatcheries, bivalve hatcheries and oyster depuration facilities. The present invention provides for the enhancement of the aquaculture industry by providing high quality protein to seed stock, oysters, shrimp and prawns. Seed stock and broodstock produced using the present system provides a valuable resource for revitalizing disease-threatened oyster and marine shrimp farms.
The present invention is a method for the continuous culturing of microalgae. The steps of the present method include providing a single container, providing a culture medium having an aqueous medium and a seed stock of the microalgae in the container, exposing the culture medium to light, maintaining the pH of the culture medium at a fixed level, harvesting a percentage of the culture medium at a duration of a predetermined period and adding a replacement seed stock medium to an unharvested portion of the medium. The step of providing a culture medium includes establishing optimal culture concentrations of constituent elements of the aqueous medium. The constituent elements include, but may not be limited to, nitrogen, phosphorous, vitamin B12, iron chloride, copper sulfate, silicate and Na2EDTA. The starting concentrations of at least one of the constituent elements is established at an optimal level. In preferred embodiments, the microalgae is Chaetoceros sp. microalgae and the constituent elements of the aqueous medium have a starting nitrogen concentration of at least about 3.0 mg N/liter, a starting phosphorous concentration of at least about 2.75 mg P/liter, a starting vitamin B12 concentration of at least 5 about micrograms/liter, a starting iron chloride concentration of at least about 0.3 mg/liter, a starting copper sulfate concentration of at least about 0.01 mg/liter, a starting silicate concentration of at least about 10 mg SiO2/liter, and a Na2EDTA concentration of about 5 mg/liter. The pH of the medium is preferably maintained at a fixed level of about 8.2. In one preferred embodiment, the pH level is maintained by introducing carbon dioxide to the medium.
Preferably, about 90% of the culture medium is harvested each period. The harvested portion is replaced with seed stock of microalgae, which is preferably seawater. A preferable harvesting period is about twenty-four hours.
The culture medium is preferably exposed to full strength direct sunlight.
Preferably, the single container is a tank having an open top. In preferred embodiments, the tank is generally cylindrical, has a diameter of about 18 inches and a height of about five feet, and is made of fiberglass.
A culture medium for growing Chaetoceros sp. microalgae preferably includes a starting nitrogen concentration of at least about 3.0 mg N/liter, a starting phosphorous concentration of at least about 2.75 mg P/liter, a starting vitamin B12 concentration of at least about 5 micrograms/liter, a starting iron chloride concentration of at least about 0.3 mg/liter, a starting copper sulfate concentration of at least about 0.01 mg/liter, a starting silicate concentration of at least about 10 mg SiO2/liter, and a Na2EDTA concentration of about 5 mg/liter, and wherein the medium has a pH maintained at a fixed level of about 8.2.
An open, continuous marine microalgae culture system includes a container, a culture medium positioned in the container and a light source for directing light rays to the culture medium in the container. The culture medium further includes an initial aqueous medium and a seed stock of microalgae. The aqueous medium further includes starting constituent element concentrations that are optimal for growing the microalgae. A harvester for removing a percentage of grown microalgae from the culture medium may also be included.